66 



FOSSIl rURTLES OF NORTH AMERICA. 



Mexico. The specimen is not quite complete, being somewhat crusht and fractured and 

 ha\ ing a portion of the margin of the left side missing. 



The species closely resembles the others of the genus, but possesses sufficiently distinctive 

 characters. The specific name is that of the stream near which the specimen was found. The 

 catalog number is 1203, of the American Museum of Natural History. 



All traces of the sutures between the bony elements of the shell are obliterated thru co- 

 ossification. The sutures between the epidermal scutes are distinct, but narrow and only 

 moderately imprest. The total length of the carapace (plate II, fig. 1; text-tig. 42) is 381 mm. 

 In the midline the length is about 12 mm. less, on account of the slight emargination in front 

 and the excavation in the rear. The breadth was close to 300 mm. The carapace is broad, 

 ovate, obtuselj pointed in front, truncate behind. On each side of the anterior emargination 

 the bolder was gently repand. The hinder border, on each side of the excavation for the tail, 

 w .is scallopt. On the hindei most part of the carapace there is a moderate rounded keel. From 

 this there may be traced forward faint indications of the two parallel grooves so distinct in 

 />'. arenosa. Except these grooves, the ornamentation seen in the latter species is absent. 



42. 



+3- 



Figs. 42 vnd 4;. Ba'ena escavada. Type. Xj. Form of shell and the scute .mas. 



42. Carapace. 45. Plastron. 



1 he must distinctive character ot this species is seen in its narrow and spatulate anterior 

 plastral lobe (plate 11, fig. 2; text-fig. 43). The plastron as a whole is relatively small. The 

 total length is 295 mm. The anterior lube has a length of 83 mm. and a breadth, at its base, of 

 96 mm. From the base the lateral borders run forward and inward to within 30 mm. of the 

 front, at the ends ol the sutures between the gular and humeral scutes. Here the width is 61 

 mm. Beyond these points the lobe expands again to (14 mm.; then curves forward and inward 

 to the ends ot the intergulai sutures. The extreme end of the lobe is truncated and falls about 

 jo mm. short o( the anterior border of the carapace. 



I he posterior lobe has a width of 1 14 mm. at the base and a length of 75 mm., failing to 

 reach the excavation in the carapace by about 47 mm. It narrows, as it passes backward, more 

 rapidl) than does that oi B.aren Hie hinder border is slightly concave. 



The bridge has a width of 135 mm. Its length, to outer margin of the shell, is 105 mm. 



